According to one known method, spent fuel rods are placed in a container of copper and embedded in lead in the container by pouring molten lead into the container and allowing it to solidify in the container. After that, the container is provided with a lid of copper which is welded to the container to form a gas-tight joint.
The present invention is based on the realization that considerable advantages can be gained if a copper powder is used instead of lead for embedding the spent fuel rods in the container and if the sealing of the container and the lid is carried out by means of isostatic compression. One advantage is that the resistance to corrosion attack is increased by the fact that the coherent mass of copper, formed from the copper powder, the container and the lid, is more resistant to corrosion than a container of copper and a body of lead within the copper container. This is due, on the one hand, to copper in itself being more resistant than lead and, on the other hand, to the protection afforded by having a coherent mass of a single material. Another advantage is that the interior of the container can be made free from cavities, which is hardly possibly when casting lead into the container and subsequently welding a lid onto the container. A further advantage is that the joint between the container and the lid after the isostatic compression is absolutely tight and completely reliable. This is because the container and the lid become a single entity without any joint, or any transition area of a different material composition existing between them. Welding together copper parts having substantial wall thicknesses, as in the known case, involves considerable difficulties and results in a joint in which the copper has a structure different from that of the adjacent material. The joint can therefore represent a weak part in the sealed container.